Some general notes: The development of electrical bomb fuzes in Germany can be traced back to 1926. Under direction of Dr. H. Rhulemann it was carried out at the Rheinmetal Borsig factory. The original goal was to develop an electrical time fuze for artillery shells that could be set at the moment of firing. Somewhere down the path of development work started on Electrical bomb fuzes. This to such satisfaction that the Luftwaffe adopted the Electrical bomb fuze in 1937. The design of most Electrical fuzes is generally the same; an aluminium outer housing, to be devided in an upper and lower housing. The upper housing has a shoulder with a locating pin, enshuring that the fuze is placed in the right direction. On top is the fuze head with the electrical plugs. The upper part normally contains the horizontal - and vertical trembler switches, resistances and the depressable pistons of the electrical plug. The lower part normally contains the condensers, the delay devices (either pyrotechnic, either mechanical) and the anti disturbance devices. The gaine is screwed in the base of the fuze. The advantages of electrical fuzes are: Easy manufacturing (low number of different components for many different functions), great flexebility, instant action, low number of duds, arming only after the pilot connects the master switch, very safe. Extensive test with electrical fields around the fuze, up to 2.000.000 volts (ligtning), showed that an electric fuze, when propperly designed, is absolutely safe. One feature of German bombs is the way the fuze pocket is placed, mostly not in the longtudinal centreline (like allied bombs), but mostly in the side, perpendicular to the centerline.
Description of the fuze: The El.Zt.Z. 9 is a electrical time fuze, used to open the ABB500 M10 boden container (cluster bomb body containing SD1 bombs), the Mk500 boden 6SD2 (body of a clusterbomb containing 9 or 15 candle flares and 6 SD2 bombs) , as well as the ignition of several types of parachute flares and photoflash bombs. The fuze is coloured red, the normal colour for Electrical time fuzes (El.Zt. Z.).
Functioning of the fuze: The fuze is made of an upper and lower body. The upper body (1) contains the depressable pistons (4), used to charge one of the two -wrapped around another- condensers (7), by one of the two depressable pistons (4)(in lowered position when the charging head is connected in the airplane, the condenser circuit -U- is in use). The rest of the top part (1) is filled by a white plastic mould (3), containing three resistances (15) and the wiring of the fuze. The lower part (2) contains a big condenser, connected to the base plate (11). It also contains a glow tube (8 )(think of a neon tube). When one of the condensers is charged in the plane, it can be done at 150 volts or at 240 volts, depending if bombing is done in level flight (150 v), or dive bombing (240 v). The amount to which the condenser (7) is loaded descides the time lapse before the glow tube (8 ) passes the current and the match composition (9) is ignited, on it's turn igniting the firing cap (10). The glow tube (8 ) should in fact be seen as a predescessor of the neon tube lamp. It is an argon filled glass tube with two opposite contact points. When the voltage on the firing condenser builds up to the required figure, the argon gas in the glow tube ionises, and allows the charge to pass into the match composition. When the bomb is dropped, the charging head is pulled off, the depressable pistons rise and the circuit where the condenser is connected with the glow tube is closed -L-. The flame of the firing cap (10) ignites the Kz Zdlg.(Kurze Zundladung / short booster) C/98 (12). The Booster is made of an aluminium can, containing 17 grams of Np (Nitropenta)10 (pink). In top of the fuze a sprengkapsel (detonator) 38 (13) is placed. A leather washer with a celluloid disc is placed above the detonator, the aluminium can is rimmed over the leather washer to close the booster. The booster is placed in the gaine (14), which is screwed in the base (11) of the fuze. A pointed screw (5) is placed in top of the fuze and is placed in a connection slider block (6). According to descriptions in books , this in fact should be a third depressable piston, used for ''testing purposes only''. As this piston, according to the drawing is only a disconnect to mass switch, I suppose the screw has the same function. Taking it out disconnects to mass. A good comparison about the functioning of this fuze is a neon tube light. As soon as you turn the switch on the wall, it takes a few seconds before it flicks on. Changing the strength of the voltage used and/or the capacity of the condenser at the end of the lamp will influence the time lapse to flick on. In case of the fuze, flick on means ignition. With Regards, Pzgr40.